1. Field of the Invention
The present invention relates to wireless communication apparatuses and more specifically to a wireless communication apparatus including a communication system preferably for use in an RFID (Radio Frequency Identification) system and a communication system such as a cell phone, and relates to an antenna device which is used for an RFID system in the wireless communication apparatus.
2. Description of the Related Art
In recent years, as an information management system for articles, the RFID system has been in practical use which establishes communication between a reader/writer for generating an induced magnetic field and an RFID tag (also referred to as “RFID device”) in which predetermined information is stored and which is attached to an article in a non-contact fashion with the use of an electromagnetic field in order to transmit the predetermined information.
As the RFID device, for example, the device disclosed in Japanese Patent No. 4069958 is known. This RFID device includes a wireless IC, a feeder circuit board including a resonance circuit which has a predetermined resonant frequency, and a radiation plate. The frequency of transmission signals and/or reception signals substantially corresponds to the resonant frequency of the resonance circuit. The resonance circuit may also function as a matching circuit for matching the impedance of the wireless IC and the impedance of the radiation plate.
By the way, in recent years, incorporating an RFID communication system into a cellular communication device, such as a cell phone, a smartphone, or the like, has been realized. In this case, when a transmission wave of the cellular system is input to the RFID device, there is a concern that the wireless IC of the RFID system is driven and spurious radiation occurs. Particularly, in the GSM (registered trademark) system, the frequency band used is near to the frequency used in the RFID system, and therefore, the transmission wave is readily input to the wireless IC of the RFID. Furthermore, since the transmission power is large, spurious radiation generated by the RFID device is large.
That is, there is a problem that part of transmission signals of the cellular system, such as the GSM, flows into the RFID device so that the characteristic (communication sensitivity) of the transmission signals deteriorates. Harmonics in the 900 MHz band are used in other systems, such as GSM 1800 and W-LAN, in many cases, and there is another problem that spurious radiation from the RFID device becomes noise and causes adverse effects on those systems.